This is Steven Salzberg's blog on genomics, pseudoscience, medical breakthroughs, higher education, and other topics, including skepticism about unscientific medical practices. Here's where I can say what I really think about abuses and distortions of science, wherever I see them.

Coffee causes cancer. Coffee prevents cancer. Who to believe?

California might soon start requiring Starbucks to warn its customers that coffee causes cancer. Has California gone nuts, or is there something to this?

A lawsuit filed in 2010 by a group called the Council for Education and Research on Toxics is in its final stages, and the judge might rule soon unless the plaintiffs settle the case. Several of the plaintiffs, including 7-Eleven, have already settled and agreed to post warnings in their stores.

The basis for the lawsuit is that brewing hot coffee produces acrylamide, which is on a list of substances that California claims cause cancer or reproductive toxicity. (It's a very long list.) Even though acrylamide has been on the list since 1990, it wasn't until 2002 that Swedish scientists discovered that acrylamide is present in many foods.

"Acrylamide is found mainly in plant foods, such as potato products, grain products, or coffee. Foods such as French fries and potato chips seem to have the highest levels of acrylamide."

Uh oh. Coffee, french fries, and potato chips. Where's the joy in life without these?

But wait a second: how come people aren't keeling over with cancer left and right, especially in our coffee-loving, french-fry-loving society? (And what about the French?)

It turns out the evidence against acrylamide is pretty sketchy. If you give it to mice in the lab, at doses 1000 times greater than the amounts found in food, it does seem to increase their risk of cancer. But mice are not people, and 1000 times is a whole lot of acrylamide. The ACS concludes that

"it’s not yet clear if acrylamide affects cancer risk in people."

It's just as easy to find claims that coffee prevents cancer. A 2017 review found that one cup of coffee a day is associated with a slight reduction in the risk of liver cancer and endometrial cancer. A 2010 review of over 500 studies found the same reductions, but a slight increase in the risk of bladder cancer among heavy coffee drinkers. Another large review in 2017, by Robin Poole and colleagues in the UK, found not only a reduced risk of cancer, but a reduction in heart disease and overall mortality.

The Poole study concluded:

"Coffee consumption seems generally safe within usual levels of intake, with [the] largest risk reduction for various health outcomes at three to four cups a day, and more likely to benefit health than harm."

Coffee lovers, rejoice! But let's not kid ourselves: no one is drinking coffee for its health benefits, are they? The stuff just tastes good.

"If coffee is deemed carcinogenic, then the State of California will be required to give up all pretense at common sense and sanity."

An afterthought: the lawsuit may be just about money. As Bloomberg News explained last October, in a story about the California coffee case: "Unfortunately, it is very easy for ‘bounty hunters’ to file Prop. 65 lawsuits against even small businesses and the cost of settlement and defense often exceeds other types of abusive litigation." The American Council on Science and Health was even more blunt, calling it an attempt to grab "a giant bag of money."

Let's hope the judge in the California case pays attention to the science. Meanwhile, the rest of us can focus on more important questions, such as: dark roast or light? French press or drip?